HeapCompact: don't cast to BasePage before sanity check.

third_party/WebKit/Source/platform/heap/HeapCompact.cpp

Index: third_party/WebKit/Source/platform/heap/HeapCompact.cpp
diff --git a/third_party/WebKit/Source/platform/heap/HeapCompact.cpp b/third_party/WebKit/Source/platform/heap/HeapCompact.cpp
index 2b68cd2107dd275641df2aa7645b888d80f71db4..e400ece5568615a8426f3a86c8540f53714ff182 100644
--- a/third_party/WebKit/Source/platform/heap/HeapCompact.cpp
+++ b/third_party/WebKit/Source/platform/heap/HeapCompact.cpp
@@ -83,10 +83,10 @@ class HeapCompact::MovableObjectFixups final {
     // derive the raw BasePage address here and check if it is a member
     // of the compactable and relocatable page address set.
     Address slotAddress = reinterpret_cast<Address>(slot);
-    BasePage* slotPage = reinterpret_cast<BasePage*>(
-        blinkPageAddress(slotAddress) + blinkGuardPageSize);
-    if (LIKELY(!m_relocatablePages.contains(slotPage)))
+    void* slotPageAddress = blinkPageAddress(slotAddress) + blinkGuardPageSize;
+    if (LIKELY(!m_relocatablePages.contains(slotPageAddress)))
       return;
+    BasePage* slotPage = reinterpret_cast<BasePage*>(slotPageAddress);

[sof, 2017/02/03 16:04:57]

nit: now only used if DCHECK_IS_ON().

 #if DCHECK_IS_ON()
     DCHECK(slotPage->contains(slotAddress));
 #endif
@@ -245,7 +245,7 @@ class HeapCompact::MovableObjectFixups final {
   HashMap<MovableReference*, Address> m_interiorFixups;
 
   // All pages that are being compacted.

[sof, 2017/02/02 22:04:41]

Could you update the comment to say that the void* points to the start of a
BasePage? "page" is a bit generic.

[krasin1, 2017/02/02 22:19:09]

Is it better now?

[sof, 2017/02/03 16:04:57]

Much better, thanks :)

-  HashSet<BasePage*> m_relocatablePages;
+  HashSet<void*> m_relocatablePages;
 
   std::unique_ptr<SparseHeapBitmap> m_interiors;
 };